I'm finally writing this after a couple of "incidents" with a couple of potential night owl apprentices. In the first case, after quite a bit of my lecturing on Linux I started sassing codename "Mr. P" when he didn't install Linux. Perhaps he was not adequately warned about my fanaticism on the matter.
A few minutes ago, I was asking an artistic web designer and potential "heavy tech" apprentice whether she'd ever run her own web server. She had not, and then I asked her what OS she's running. The answer was (queue horror music) "Windows." Then I asked her whether I'd given her my open source lecture yet. I had not, so I figured it was time to write it out once and for all.
As I understand the history, "free-as-in-speech" software came before "open source." For purposes of this discussion, I'm generally going to conflate "open source," "free as in pizza (or beer)," and "free as in speech." There are differences, but that's another topic.
With that said, I need to give a basic definition of "open source," starting with "source." The "source code" is what (almost) every piece of software is written in. It's the semi-English "if"-"then"-"else"-"for"-"function" statements of software / programming languages. Without the source code, it's difficult to modify existing software.
Open source means that the source code of the software you're running is freely and legally available for study, modification, and distribution (of the original or modifications).
Starting from a very practical perspective, why would I want my livelihood dependent on expensive software with complex licenses and complex license enforcement? The Linux operating system is free-as-in-beer (or pizza). It does everything Windows can do and more, and I can freely and legally download it, install it, run it, copy it, and distribute it. If my computer dies, I'm not worried about obtaining a new license before I can get going again.
Chrome and Firefox run in Linux, and (free) Libre Office comes with Ubuntu Linux desktop. Libre Office has a spreadsheet, word processor, and other elements of MS Office. It can read and write to MS Word format and other relevant formats.
For my professional purposes, the entire Linux Apache MySQL PHP (LAMP) "stack" is free. The NetBeans IDE / debugger is free. I can do all my work with freely available software. I never have to worry about licensing or downloading any of the software I need.
I'm an Ayn Rand-ite Objectivist. There's nothing wrong with Microsoft or Apple making money on software. However, given that there are good-to-better open source options for pretty much any type of software, why should I spend my money to help them make money?
The open source ethos is an example of a post-scarcity economy. The most popular example of post-scarcity is Star Trek: The Next Generation. In that universe, money barely exists because everything is so easily available that there is no need to ration it with money. Gult's Gulch in Rand's Atlas Shrugged was essentially post-scarcity, but they used money more as a matter of principle than anything.
Another way of putting this is given that we can copy software extremely cheaply, why not take advantage of that feature and make software post-scarcity?
I've had to "hack" the core of both Drupal and OpenERP (Odoo) to fix bugs that were in my way and thus annoying me. Because they are open source, I have the ability to do that. With a closed source / proprietary system, I would be waiting indefinitely for the manufacturer to help me. Or I could very tediously de-compile their executable (binary) code, but that's generally illegal and / or against the license.
On that point, if a system catastrophically fails, I have the freedom to personally or with delegation diagnose and fix the problem rather than being dependent on the manufacturer.
You don't have to be a developer to care about this. If you depend on software, you should feel better knowing that you can scour the world to find someone to help you faster than "official" support can. And the talent pool to scour is tremendously larger because there are relatively speaking a lot of people who can figure out a system with its source code.
There is plenty more to say on this, but this'll do for a start. Here are a couple of topics I started to address and will likely come back to:
I lived long enough to see the cure for death; to see the rise of the Bitchun Society, to learn ten languages; to compose three symphonies; to realize my boyhood dream of taking up residence in Disney World; to see the death of the workplace and of work.